Atmospheric pressure ionization/mass spectrometers are configured to introduce ions generated at atmospheric pressure into a vacuum system to analyze the mass of the ions. Atmospheric pressure ionization includes electrospray ionization (ESI) (hereinafter called “ESI”) and atmospheric pressure chemical ionization (APCI) (hereinafter called “APCI”), for example.
The ESI is a technique of passing a sample solution through a capillary, to which high voltage is applied, for spraying to generate charged droplets, and creating ions through repetitive evaporation and breakup of these charged droplets. The ESI is an ionization scheme capable of treating a high-molecular weight sample, a highly-polar sample or the like. In the ESI, a technique of spraying a large amount of heated gas is typically used in combination to promote evaporation and vaporization of the droplets.
The APCI is a technique of heating a sample solution for vaporization, and ionizing the obtained solvent molecules through corona discharge. In the case of this technique, electrical charge is transferred between the primary ions generated by the corona discharge and sample molecules, whereby the sample molecules are ionized. The APCI can be used for a low-molecular weight sample having a smaller molecular weight or a low-polarity sample having smaller polarity than the ESI.
Patent Literature 1 and Patent Literature 2 describe a technique of improving the performance of the APCI. In this technique, the direction of introducing sample gas obtained by vaporization of a sample solution into a corona discharge area and the ion traveling direction are inverted. This lowers the reaction efficiency between the primary ions generated by the corona discharge and an inhibitory factor present in the atmosphere. As a result, generation of noise ions can be suppressed. This also can improve the reaction efficiency between the primary ions and the sample molecules, and so increase the detected intensity of generated ions.
When such ionization schemes treating different samples and being based on different principles (e.g., the ESI and the APCI) can be implemented with one ion source, then the range of substances to be measured and the application range of the ion source can be expanded. The present specification refers to the ion source supporting a plurality of types of ionization schemes as a hybrid ion source.